In clinical diagnosis, the determination of iodide in the urine plays an important role in monitoring the function of the thyroid gland. The determination of iodide in foodstuffs and fodder is also becoming increasingly important. Suitable rapid methods which can be used routinely have hitherto not been described for the determination of iodide in urine.
In most known methods, a pretreatment of the urine is carried out either by treatment with a strong acid or by ashing at high temperatures. This is followed by the determination of iodide by measurement of the reduction of cerium (IV) ions to cerium (III) ions by the catalytic action of iodide (Sandell-Kolthoff reaction). The pretreatment with strong acids (potassium chlorate in 70% perchloric acid) or the dry ashing of the urine with potassium carbonate serves to remove substances which can interfere in the reduction of the cerium ions. This results in the formation of toxic perchloric acid vapors and the perchlorates which are likewise formed are known to be explosive.
Anal. Chim. Acta 282, 87 (1993) describes a method for the determination of iodide using chlorpromazine and hydrogen peroxide, but this is very susceptible to interference by many substances which occur especially in urine and also in foodstuffs and fodder. Furthermore, DE-A 37 43 224 discloses a method for the determination of peracids, wherein a chromogen and iodide are added to the sample solution. However, those skilled in the art could not deduce from this publication that this reaction can be used for the detection of iodide.